Wiper control apparatus

ABSTRACT

A wiper control apparatus includes a combination switch  2 , a wipermotor  7 , an autostop (AS) switch  8 , a first semiconductor switch element  4  for on/off controlling energization of the wiper motor, a second semiconductor switch element  5  for turning on a closed circuit which passes a reverse current through the wiper motor  7  while the energization for the wiper motor  7  is off, a controller for ON/OFF controlling the first and the second semiconductor switch element, and a current limiting resistor R 1  for limiting the current flowing the second semiconductor switch element  5 . In this configuration, a wiper control apparatus can be provided which can solve the problem when the abnormality of short-circuiting downstream of the wiper motor occurs, is compact, reliable and surely operable using semiconductor switches and a digital-controlled controller.

BACKGOUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiper control apparatus using asemiconductor switching element such as a MOSFET.

2. Description of the Prior Art

One of previously known wiper control apparatus is disclosed inJP-A-9-193748. In this wiper control apparatus, as seen from FIG. 13,when a combination switch 17 is set at an intermittent mode (INT), adriving circuit 20 turns on an interruption switch MOSFET 19 to start amotor 15 so that a wiper reciprocates once. Then, the terminals P and Qof a wiper switch 16 are connected to each other. Then, the drivingcircuit 20 turns off the interruption switch 19 to interrupt the powersupply to the motor 15. When the terminals P and Q of the wiper switch16 are connected, a battery-voltage side terminal K and a ground sideterminal J are connected to each other through a contact terminal T1 andbraking resistor 18 so that the motor 15 is braked. Thus, the wiperstops quickly.

However, the wiper control apparatus presents the following problems.

(1) When the wiper motor 15 generates an abnormal current as if it islocked, a large current continues to flow through a MOSFET 19 orresistor 18. Therefore, the resistor 18 or MOSFET 19 may be excessivelyheated and burned. In order to avoid the burning, a countermeasure forsetting a large current rating for the resistor 18 and MOSFET 19 andproviding a radiator is required. This upsizes the apparatus and makesit expensive.

(2) When the plus terminal and minus terminal of a battery 11 areerroneously connected inversely, a large current continues to flowthrough the parasitic diode of the MOSFET 19 and the resistor 18.Therefore, the resistor18 and the MOSFET may be burned.

(3) For some time after the MOSFET 19 turns on, since the terminals Pand Q of the wiper switch 16 remain connected, a tunneling current willflow through a passage of wiper switch 16→resistor 18→MOSFET 19 from thebattery 11. This leads to unnecessary dissipation of heat and noise.

(4) Setting the intermittent time and the after-wash wiping operationtime after the washer has been operated is carried out in an analogmanner using the charging/discharging theory of a capacitor. This leadsto a large change in these times.

In order to solve the problems (1) to (4) of the above wiper controlapparatus, JP-A-2000-335374 proposed a wiper control apparatus which iscompact, reliable and surely operable using a semiconductor switch and adigital controller.

In the proposed wiper control apparatus, also when the abnormality ofthe wiring downstream of the wiper motor 15 being short-circuited to achassis (ground)occurs, a large current continues to flow through theresistor 18 so that the resistor may be excessively heated and burned.

Now it is assumed that short-circuiting of the wiring to the chassis(ground) has occurred between the ground side terminal J and thecombination switch 17. In this case, a current flows via thebattery-voltage side terminal K of ground side terminal J of the wipermotor 15 and the short-circuited point so that the wiper motor 15rotates.

On the other hand, the contact P of the wiper switch 16 is periodicallychanged between the contact points Q and R. While the contact P is beingin contact with the contact Q (about 0.1 sec), a large current flows viathe contact P, resistor 18, combination switch 17 and short-circuitedpoint. This also occurs between the combination switch 17 and the switchdevice 19 and between the combination switch 17 and the resistor 18.

At this time, since the current is limited by the resistor 18 having aresistance of 2-4Ω (if the voltage of the battery 11 is 12 V, thecurrent is 5 V at the maximum) , the fuse will not be broken. As aresult, the current continues to flow through the resistor 18 so that itmay be excessively heated and burned. In order to avoid the burning, thecountermeasure of providing a radiator with the current rating of theresistor 18 being increased is required. This increases the scale of theapparatus and the production cost thereof.

FIG. 13 shows timing charts of signals in an ignition switch (IG) of awiper control apparatus 12, a motor AS switch 16, wiper motor 16 andbrake resistor 18. As seen from FIG. 14, when abnormality ofshort-circuiting occurs downstream of the wiper motor 15, a currentcontinues to flow through the wiper motor 15 so that the contact pointof the motor AS switch 16 is periodically changed between the high sideand low side. Correspondingly, the current continues to flow through thebraking resistor 18.

SUMMARY OF THE INVENTION

An object of the present invention is to improve the wiper controlapparatus proposed in JP-A-2000-335374 and to solve the problem whenabnormality of the wiring downstream of a wiper motor beingshort-circuited occurs in the conventional wiper control apparatus toprovide a wiper control apparatus which is compact, reliable and surelyoperable using a semiconductor switch and a digital controller.

In order to attain the above object, in accordance with the first aspectof the present invention, there is provided a wiper control apparatuscomprising:

a combination switch for setting an operation mode of a wiper;

a wiper motor which is driven according to the operation mode set by thecombination switch;

an autostop (AS) switch for producing a signal having a level varyingaccording to a park position and other positions as the wiper motorrotates;

a first semiconductor switch element for on/off controlling energizationof the wiper motor;

a second semiconductor switch element for turning on a closed circuitfor braking the wiper motor which passes a reverse current through thewiper motor while energization for the wiper motor is off;

a controller for supplying a first ON/OFF control signal to the firstsemiconductor switch element and a second ON/OFF control signal to thesecond semiconductor switch element; and

current limiting means for limiting a current flowing through the secondsemiconductor switch element.

In this configuration, since an abnormal current is limited whenabnormality of short-circuiting occurs downstream of the wiper motor,the safety of the wiper control apparatus can be improved. Since heatgeneration can be reduced when the apparatus is in a normal operationand abnormality of short-circuiting occurs, the wiper control apparatuscan be downsized.

Preferably, the controller monitors a level change in a signal from theautostop (AS) switch and where the level change occurs while the wiperstops, the controller interrupts the second ON/OFF control signal whenthe number of the level changes reaches a prescribed number of times.

In this configuration, where the abnormality of short-circuiting occursdownstream of the wiper motor so that a short-circuiting current flowsthrough the semiconductor switch device for turning on/off the brakingcircuit, since the braking circuit is surely interrupted, the safety ofthe wiper control circuit can be improved.

Preferably, the first semiconductor switch element is an N-channelMOSFET, and the second semiconductor switch element is a P-channelMOSFET.

In this configuration, the wiper control apparatus can be downsized andmanufactured at low cost.

Preferably, a Zener diode is connected to the semiconductor switchelement.

In this configuration, inverted electromotive force when the firstsemiconductor switch is excessively heated and cut off and interruptedis dissipated. The first semiconductor switch can be protected when abattery is erroneously connected in a reverse direction. The secondsemiconductor switch element can be surely turned off in a manner ofshifting the electric potential of its gate electrode.

Preferably, the first semiconductor switch element is located downstreamor upstream of the wiper motor.

Where the first semiconductor switch element is arranged upstream, it isprotected from malfunction such as short-circuiting so that the safetyfor the apparatus is improved.

Preferably, the wiper control apparatus according to any one of thefirst to fifth aspects can be employed together with a relay-type wipercontrol apparatus, and the controller controls the operation of bothwiper control apparatus and relay-type control apparatus.

In this configuration, the controller includes the collected function ofcontrolling both the semiconductor switch(s) and relay, and hencedown-sized and made inexpensive. The control is correlated between thefront wiper and rear wiper.

The above and other objects and features of the present invention willbe more apparent from the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of the wiper controlapparatus according to the present invention;

FIG. 2 is a block diagram of a typical configuration of the controllerin a wiper control apparatus of FIG. 1;

FIG. 3 is a circuit diagram of another embodiment of the wiper controlapparatus according to the present invention;

FIG. 4 is a circuit diagram of an actual configuration of an overheatinginterruption/protection circuit in FIG. 4;

FIG. 5 is a timing chart of signals at respective points of thecontroller during the INT mode in the wiper control apparatus in FIG. 1;

FIG. 6 is a timing chart of signals at respective points of thecontroller during the ON mode in the wiper control apparatus in FIG. 1;

FIG. 7 is a timing chart of signals at respective points of thecontroller during the WASH mode in the wiper control apparatus in FIG.1;

FIG. 8 is a timing chart of signals at respective points of the wipercontrol apparatus for explaining the protection operation in the wipercontrol apparatus in FIG. 1;

FIG. 9 is a block diagram showing another embodiment of the wipercontrol apparatus according to the present invention, i.e. a two-speedwiper motor control apparatus;

FIG. 10 a block diagram showing still another embodiment of a wipercontrol apparatus according to the present invention, i.e. a combinationwith a relay wiper control apparatus;

FIG. 11 is a circuit diagram showing a further wiper control apparatusaccording to the present invention;

FIG. 12 is a circuit diagram showing the configuration of a conventionalwiper control apparatus;

FIG. 13 is timing charts of the respective parts in the wiper controlapparatus shown in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to the drawings, an explanation will be given of severalembodiments of a wiper control apparatus according to the presentinvention.

FIG. 1 is a block diagram of an embodiment of the wiper controlapparatus according to the present invention. The wiper controlapparatus includes a control unit, generally 1, a wiper motor 7, an AS(autostop) switch 8 and a washer motor 9. The control unit 1 includes acombination switch 2, a controller 3, MOSFETs 4, 5, Zener diodes 6, 6 a,6 b, 6 c and a current limiting resistor R1.

The combination switch 2 serves to set various operation modes of awiper by an operation by a vehicle driver. The combination switch 2permits the operation modes of the wiper, i.e. an OFF (stopping) mode.,INT (intermittent operation) mode, ON (continuous operation) and WASH(washing) mode to be made through a combination of connection of an ONterminal, an INT terminal, GND terminal and a WASH terminal. Thecombination switch 2 also includes a VR terminal for connecting avariable resistor 10 for setting an intermittent time.

The controller 3, whose typical configuration is shown in FIG. 2,includes a digital control unit 3A, a 5 V regulator 3B, a reset circuit3C, an oscillation circuit 3D, an input circuit 3E, a level shiftcircuit 3F and a VR conversion circuit 3G, an MOSFET gate drive 3H and acurrent detecting circuit 3I.

The digital control unit 3A, which is constructed of e.g. amicrocomputer, serves to control the entire operation of the wipercontrol apparatus.

The 5 V regulator 3B, to which a battery power supply voltage (e.g. 13.5V) is supplied through an IG (ignition) switch 12 and a fuse 13 from abattery 11 which is a power source for a vehicle, serves to supply adriving voltage, e.g. 5 V for the digital control unit 3A.

The reset circuit 3C, when the power for the wiper control apparatus isturned on by turn-on of the IG switch 12, serve to reset the operationof the digital control unit 3A.

The oscillation circuit 3D serves to generate and supply a clock signalfor the digital control unit 3A.

The input circuit 3E serves to detect the on/off of each of the INTterminal and ON terminal of the combination switch 2 and supply an INTmode ON signal and an ON mode ON signal to the digital control unit 3A.

The level shift circuit 3F converts the battery power supply voltage(13.5 V) , detected at the WASH terminal of the combination switch 2 andthe common terminal of the AS switch, into 5 V to be supplied to thedigital control unit 3A.

The VR conversion circuit 3G is connected to the VR terminal of thecombination switch 2, and serves to set the intermittent time during theINT mode. A typical configuration of the VR conversion circuit 3G isshown in FIG. 12.

The MOSFET gate drive 3H converts the digital output for controlling theMOSFET produced from the digital control unit 3A into an MOSFEToperation level voltage which is outputted at control output terminalsFET-a and FET-b.

The controller 3, under the control by the digital control unit 3A,performs an excellent timing control function during each operation modeon the basis of the timing charts as shown in FIGS. 5-7. The timecontrol function has the characteristic functions listed as follows.

(Function A): function of forwarding the operation to the control unitsFET-a and FET-b with a time difference tb.

(Function B): function of continuing to produce the control output FET-auntil the wiper returns to a park position when the combination switch 2is turned off on the way of the wiper operation, for example.

(Function C): function of precisely defining the after-wash wiping afterthe wash operation by the number of times thereof.

(Function D): function of precisely defining the number of times ofafter-wash wiping even when the combination switch is changed from ONinto OFF during the after-wash wiping after the wash operation.

(Function E) function of converting the resistance of a variableresistor 10 in a digital value to define the intermittent timeprecisely.

(Function F): function of monitoring the level of the AS signal, anddeciding that short-circuiting has occurred downstream of the wipermotor when the AS signal repeats high level→low level→high level→ . . .in a state where INT, WS, ON are not received or the control outputFET-a is not produced.

The details of each function will be explained later.

The MOSFET 4 is an N-channel type MOSFET that is a first semiconductorswitching device, and serves as a semiconductor switch element forsupplying or interrupting the driving voltage to the wiper motor 7 bymeans of its ON/OFF. The drain thereof is connected to the wiper motor7, source thereof is connected to the GNT terminal of the combinationswitch 2 and ground, and the gate thereof is connected to the controloutput terminal FET-a of the controller 3.

The MOSFET 5 is a P-channel type MOSFET which is a second switchingdevice, and serves as a semiconductor switch element for performing thebraking operation of the wiper motor 7 by means of its ON/OFF. The drainthereof is connected to a fuse 13 through a shunt resistor RS1, thesource thereof is connected to the drain of the MOSFET 4 through theZener diode 6, and the gate thereof is connected to the control outputterminal FET-b of the controller 3.

The Zener diode 6 is selected to have a rating defined so that the Zenervoltage satisfies a relationship: a battery voltage (e.g. 13.5 V)<Vz<therating voltage V_(DSS) of the MOSFET 4. In this way, the Zener diode 6can have three functions of dissipating the reverse electric motiveforce of the wiper motor 7 when the MOSFET 4 is overheated and broken,protecting the MOSFET 4 when the battery 11 is connected inversely dueto erroneous connection, and surely turning off the MOSFET 5 by shiftingthe gate potential by 7 V. During the normal operation, only the brakingcurrent flows through the Zener diode 6. Therefore, the Zener diode mayhave a small current of capacity so that it can be miniaturized and madeinexpensive. The Zener diode 6 is connected to the source side of theMOAFET 5 in FIG. 5 (where the withstand voltage of the control sectionis sufficiently high) , but may be connected to the drain side. TheZener diodes 6 a, 6 b, 6 c and 6 d are provided to protect the gates ofthe MOSFETs 4 and 5.

The current limiting resistor R1 serves to limit the current flowingthrough the MOSFET 5 when the short-circuiting has occurred downstreamof the wiper motor 7. The resistance of the current limiting resistor R1is set so that it does not hinder the braking operation and ashort-circuiting current is limited to be not higher than the pulsecurrent rating of the MOSFET 5.

As for the wiper motor 7, its plus terminals is connected to the fuse 13and the minus terminal is connected to the drain of the MOSFET 4.

As for the AS switch 8, as well known, as the wiper motor 7 rotates, itscommon contact a is connected to contact b (high level contact) when thewiper is at a park position, or connected to contact c (low levelcontact) when the wiper is at the other position than the park position.

As for the washer motor 9, its plus terminal is connected to the fuse 13and the minus terminal is connected to the WASH terminal of thecombination switch 2.

The normal operation of the wiper control apparatus according to thepresent invention having the configuration described above has threeoperations inclusive of an intermittent wiper operation, a continuouswiper operation and an after-wash wiping operation. The individualoperations will be explained below.

In an initial condition, the IG switch 12 is in an “ON” state and thewiper is at a park position. Therefore, the common contact a of the ASswitch 8 is connected to the contact b. The control outputs from thecontroller 3 to the FETs 4 and 5 are “HIGH” at FET-b and “LOW” at FET-aso that both the MOSFETs 5 and MOSFET 4 are “OFF”. Specifically, sincethe MOSFET 4 is an N-channel type, it turns “ON” when the control signalin a high level is supplied to the gate so that a current flows betweenthe drain and source. The MOSFET 4 turns off when the signal in a lowlevel is supplied to the gate. On the other hand, since the MOSFET 5 isof a P-channel type, it turns “ON” when the control signal in a lowlevel is supplied to the gate, and turns off when the control signal inthe high level is supplied to the gate. The control signal in the highor low level is set at a level sufficiently higher or lower than anoperation threshold value of the pertinent MOSFET.

Intermittent Wiper Operation

Referring to FIG. 1 and FIG. 5 which is a timing chart of signals atrespective points of the controller 3 in the INT mode in the wipercontrol apparatus in FIG. 1, an explanation will be given of theintermittent wiper operation.

When the combination switch 2 is changed into an INT position from theinitial state, an INT “ON” signal (low level) is supplied from thecombination switch 2 to the controller 3. When the controller 3 receivesthe INT “ON” signal, it changes the control output FET-a from a lowlevel to a high level immediately at a trailing edge of the INT “ON”signal, thereby controlling the MOSFET 4 to be “OFF”.

When the MOSFET 4 turns on, a current flows along the passage of battery11→IG switch 12→fuse 13→wipermotor 7→MOSFET 4→ground, the wiper motor 7starts to rotate. In this case, the AS switch 8, which is synchronouswith the rotation of the wiper motor 7, is changed from the high levelcontact b into the low level contact c so that the AS input to thecontroller 3 is changed from the high level into the low level. When thewiper reciprocates once on a windshield glass as a result that the wipermotor 7 has continued to rotate, the wiper returns to the park position.Then, the AS switch 8 returns from the low level contact c to the highlevel contact b and the high level signal is supplied to the AS input ofthe controller 3.

When the high level signal is supplied to the AS input of the controller3 again, the controller 3 changes the control output FET-a from the highlevel into the low level, thereby controlling the MOSFET 4 to be “OFF”.Subsequently, after dead time td elapses, the controller 3 changes thecontrol output FET-b from the low level to the high level, therebycontrolling the MOSFET 5 to be “ON”.

As the function A of the controller 3, the dead time td is set for thepurpose of preventing the MOSFET 5 and 4 from becoming “ON” and atunneling current from flowing. The dead time may be set at a timesufficiently longer than the response time of an MOSFET.

The wiper motor 7, the energization of which is stopped by OFF of theMOSFET 4, generates a reverse electromotive force. However, since theMOSFET 5 turns on, a closed loop is formed consisting of the plusterminal of the wiper motor 7→Zener diode 6→MOSFET 5→minus terminal ofthe wiper motor. Therefore, a reverse current (braking current) flowsabruptly through the wiper motor 7 to consume the reverse electricmotive force. As a result, the wiper motor 7 is braked and stopsabruptly, and hence the wiper stops without exceeding from the parkposition.

The MOSFET 5 is adapted so that only the braking current when the wipermotor 7 is stopped flows. Since the braking current flows for a shorttime of several tens of mili seconds, the R_(DSON) rating of the MOSFET5 is set at a large value of 2-20 times as large as that of the MOSFET5. For this reason, the MOSFET 5 is further down-sized and madeinexpensive.

The controller 3 places the control output FET-b at the low level onlyduring a prescribed period tb necessary to cause the braking current toflow so that the MOS-FET 5 is maintained at the ON state. After aprescribed time tb elapses, the controller 3 returns the control outputFET-b from the low level to the high level, thereby controlling theMOSFET 5 to be “OFF”.

The controller 3, after it has turned off the MOSFET 5, counts the INTtime (time while the wiper stops) set by the variable resistor 10, andcontrols the MOSFET 4 from OFF to ON again. Thereafter, the controller 3repeats the above operation. In this way, the intermittent wiperoperation is performed.

During the intermittent wiper operation, when the combination switch 2is changed from the INT position to the OFF position, the OFF signal(high level) is supplied to the INT input of the controller 3. In thiscase, if the wiper remains on the windshield glass and the AS switch 8is located on the side of the low level contact c, since the AS input ofthe controller 3 is at the low level, the controller 3 keeps the controloutputs FET-a and FET-b at the high level (above function B of thecontroller 3). Therefore, the MOSFET 4 remains ON and the MOSFET 5remains OFF so that the wiper motor 7 continues to rotate.

When the wiper returns to the park position and the AS switch 8 isswitched into the side of the high level contact b as a result that thewiper motor 7 has continued to rotate, the high level signal is suppliedto the AS input of the controller 3. Then, the controller 3 immediatelychanges the control output FET-a from the high level to the low level,thereby turning off the MOSFET 4. After the dead time td has elapsed,the controller 3 changes the control output FET-b from the high level tothe low level, thereby turning on the MOSFET 5. Thus, the wiper motor 7ceases to rotate.

When the combination switch 2 is changed from the INT position to theOFF position, if the AS switch 8 is located on the side of the highlevel contact b (and hence the wiper is at the park position) , thecontrol signal at the low level from the controller 3 is immediatelysupplied to the MOSFET 4 and MOSFET 5. As a result, the MOFET 5 becomesON and MOSFET 4 becomes OFF so that the wiper motor 7 immediately stops.

In this way, when the combination switch 2 is changed into the OFFposition, at any position of the wiper, as long as the IG switch 12 isON, the wiper necessarily stops at the park position. The AS switch 8 isonly employed to detect the park position of the wiper and no drivingcurrent for the wiper motor 7 flows through the AS switch 8. Therefore,the AS switch can employ a contact of a small-current capacity type, andmay be down-sized and inexpensive. In this case, reliability of itscontact can be improved.

The intermittent (INT) time during the intermittent wiper operation canbe set by the variable resistor 10 connected to the VR terminal of thecombination switch 2. The resistance of the variable resistor 10 isconverted into a digital value by a VR converter circuit 3G of thecontroller 3, whose configuration is shown in FIG. 12, and the converteddigital value is sent to the digital control unit 3A. Thus, theintermittent (INT) time can be defined in a precise digital manner(function E of the controller 3).

Continuous Wiper Operation

Referring to the block diagram of FIG. 1 and the timing chart of signalsat respective points of the controller 3 during this operation mode (ONmode) as shown in FIG. 6, an explanation will be given of the continuouswiper operation.

When the combination switch 2 is changed into the ON position from theinitial state, the ON signal (low level) is supplied from thecombination switch 2 to the ON input of the controller 3. Then, thecontroller 3 controls the MOSFET 5 so that it is changed from the lowlevel to the high level, and controls the MOSFET 4 so that it ismaintained at the high level. Thus, the MOSFET 5 is controlled to remain“OFF” whereas the MOSFET 4 is controlled so that it is changed from“OFF” to “ON”.

When the MOSFET 4 turns on, the wiper motor 7 starts to rotate. Then,since the AS switch 8, which is synchronous with the rotation of thewiper motor 7, is changed from the side of the high level contact b intothe side of the low level contact c, the AS input to the controller 3 ischanged into the low level. The wiper passes the park position wheneverit reciprocates once on the windshield glass. At this time, the ASswitch 8 temporarily returns to the high level contact b, and hence thehigh level signal is supplied to the AS input of the controller 3.However, the controller 3 continues to supply the control signal at thehigh level from the control outputs FET-a and FET-b to the gates of theMOSFETs 4 and 5. Therefore, the wiper motor 7 continues to rotate.

When the combination switch is changed from the ON position into the OFFposition, the OFF signal (high level) is supplied to the ON inputterminal of the controller 3. At this time, if the wiper remains on thewindshield glass and the AS switch 8 is located on the side of the lowlevel contact c, the controller 3 keeps the control signal output to theMOSFETs 4 and 5 at the high level. Therefore, the wiper motor 7continues to rotate and the wiper returns to the park position. Then,since the high level signal is supplied to the controller 3, thecontroller 3 changes the control output FET-a from the high level to thelow level so that the MOSFET 4 is immediately turned off and afterelapse of the dead time td, the MOSFET 5 is “ON” during the prescribedtime tb. Thus, the rotation of the wiper motor is stopped. The brakingoperation will be carried out in the manner described above.

After-wash Wiping Operation

Referring to the block diagram of FIG. 1 and the timing chart of signalsat respective points of the controller 3 in the WASH mode shown in FIG.7, an explanation will be given of the after-wash wiping operation.

When the combination switch 2 is changed from the OFF position into theWASH position, a current flows on the battery 11→IG switch 12→fuse13→washer motor 9→WASH terminal of the combination switch 2→GNDterminal→ground. As a result, the washer motor 9 starts to rotate. Thewasher motor 8 operates a pump (not shown) so that a washing liquid issent from a washing liquid tank (not shown) onto the windshield glass.

At this time, at the same time as energization of the washer motor 9,the ON signal (low level) is supplied to the WS input of the controller3. When a delay time ta elapses from the trailing edge of the ON signal,the controller 3 changes the control output FET-a from the high level tothe low level, thereby turning on the MOSFET 4. When the MOSFET 4 isturned on, the wiper motor 7 starts to rotate. The wiper makes areciprocating movement on the windshield glass to wash the windshieldglass by the washing liquid. During the period while the combinationswitch 2 is at the WASH position, the controller 3 continues to supplythe high level control signal to the MOSFETs 4 and 5. The delay time tais set assuming the time taken from when the washer motor 9 starts torotate to when the washing liquid reaches the windshield glass.

When the combination switch 2 is changed from the WASH position to theOFF position, the OFF signal is supplied to the WS input terminal of thecontroller 3. After the OFF signal has been supplied to the WS inputterminal, the controller 3 continues to supply the high level controlsignal to the MOSFETs 4 and 5 during a prescribed after-wash wiping timeTa, and thereafter changes the control output FET-a from the high levelto the low level so that the MOSFET 4 is turned off to stop the wiper atthe park position.

Therefore, in the after-wash wiping operation, the combination switch 2is set at the WASH position to perform the washer operation. When thecombination switch 2 is set at the OFF position to stop the washeroperation, the wiping is performed a prescribed number of times(function C of the controller 3).

On the other hand, where the combination switch 2 is changed from theWASH position to the ON position, the controller 3 continues the wiperoperation. Where the combination switch 2 is changed from the WASHposition to the ON position and further to the OFF position, if theprescribed after-wiping time does not elapse, the controller 3 controlsthe wiper to perform the after-wiping during the remaining time andthereafter stop at the park position (function D of the controller 3).In this embodiment, after the after-wiping time has been set in terms oftime, it can be set in terms of the number of times.

In the above various kinds of operation modes, the wiper controlapparatus according to the invention performs the protection operationwhen abnormality of the wiring short-circuited to the chassis (ground)has occurred downstream of the wiper motor 7 (function F in thecontroller 3).

Example of Protection Operation

Referring to the block diagram of FIG. 1 and the timing chart of signalsat respective points of the wiper control apparatus for explaining thefirst example of a protection operation shown in FIG. 8, an explanationwill be given of a protection operation by the controller 3. Thefollowing example describes the protection operation when theabnormality of short-circuiting has occurred while the wiper stops (thecombination switch 2 is at the OFF position).

Now, it is assumed that the wiring downstream of the wiper motor 7 hasbeen just short-circuited to the chassis (ground) at timing t1 in thetiming chart of FIG. 8. Then, a current flows to ground via the battery11→IG switch 12→fuse 13→wiper motor 7→short-circuiting point so that thewiper motor 7 rotates. As the wiper motor 7 rotates, the common contacta of the AS switch 8 is changed from the high level contact b to the lowlevel contact c so that the AS input of the controller 3 is changed intothe low level. When the wiper makes a round trip once, the AS input ofthe controller 3 is restored to the high level again. As long as theshort-circuiting continues, the AS input of the controller 3 alternatelyrepeats the high and low levels.

On the other hand, as seen from the above description, the controller 3has a function of driving the MOSFETs 4 and 5 so that the wiper returnsto the park position even when the combination switch 2 is OFF.Therefore, when the wiper motor rotates once and the AS switch 8 ischanged from the low level into the high level, in order to brake thewiper motor, the MOSFET 5 is turned on. At this time, a current flowsalong the passage of battery 11→IG switch 12→fuse 13→current limitingresistor R1→MOSFET 5→Zener diode 6→short-circuiting point. In this case,since the current is limited by the current limiting resistor R1, theMOSFET 5 will not be broken.

In the normal operation, the second rise of the AS signal does not come.For this reason, the controller 3 decides the second round rise of theAS signal at timing t3 abnormality and so does not produce the controloutput FET-b. At the third round of the AS signal at timing t4, thecontroller 3 produces the control output FET-b to execute retrial of thebraking operation based on turn-on of the MOSFET 5. At the fourth roundrise of the AS signal at timing t5, the controller 3 decides theabnormality of short-circuiting to interrupt and latch the controloutput FET-b.

Therefore, after the latching, even when the wiper motor 7 continues torotate and the AS switch 8 is converted from “LOW” to “HIGH”, the MOSFET5 remains OFF so that the control section 1 is protected from theabnormality of short-circuiting.

Retrial of the braking operation intends to make recovery when the ASsignal falls from “HIGH” to “LOW” because the wiper passes the parkposition owing to the incomplete braking during the normal operation.Stopping the control output FET-b at the second round intends to stopcontinuous flow of the short-circuiting current, thereby suppressing thetemperature rise in the MOSFET 5. Where the MOSFET 5 has enough currentcapacity, the number of rises of the AS signal may be simply counted sothat when any number of times (twice or more) is counted, the controloutput FET-b may be interrupted and latched.

The restoration from the latching is carried out by resetting of thecontrol unit 1, opening of the terminal of the battery 11, inputting ofa reset input from the resetting circuit 3 c, etc.

The threshold value of the current may have hysteresis. A resting timemay be given between when the threshold value of the current exceeds thethreshold value to turn off the MOSFET 5 and when the current falls toturn off the MOSFET 5 again.

The similar protection operation is carried out also when abnormality ofshort-circuiting occurs downstream of the motor and the combinationswitch 2 is turned off. Further, when the abnormality ofshort-circuiting occurs during the intermittent operation, the loadcurrent is prevented from continuing to flow.

The configuration and operation of the wiper control apparatus accordingto the present invention provides the following advantages.

(1) Since the R_(DSON) rating of the MOSFET 5 is set at a large valuewhich is 2-20 times as large as that of the MOSFET 4, the MOSFET 5 canbe down-sized and made inexpensive.

(2) Since only the braking current flows through the Zener diode 6 forcurrent blocking when the battery is reverse-connected and through theMOSFET 5, the current capacity of the Zener diode 6 can be made small.Therefore, the Zener diode can be made down-sized and inexpensive.

(3) Since the control outputs FET-a and FET-b of the controller 3 aresupplied to the MOSFETs 4 and 5 with a time difference td between theirtimes of falling, no tunneling current flows and unnecessary heat andnoise dissipation is removed.

(4) When the combination switch 2 is turned off on the way of the wiperoperation, the controller 3 continues to issue the control output FET-auntil the wiper returns to the park position in such a manner that thesignal current is caused to flow through the AS switch 8 of the wipermotor switch 7. For this reason, the AS switch 8, MOSFET 5 and Zenerdiode 6 can be down-sized and made reliable.

(5) Since the wiping after the washing has been made is definedaccurately, an error therefor can be removed.

(6) When the combination switch 2 is changed from the ON position to theOFF position during the wiping after the washing, since the number oftimes of wiping is defined accurately, an error therefor can be removed.

(7) When the abnormality of the wiper motor 7 occurs, energization ofthe wiper motor 7 is interrupted. After the abnormality is removed, theenergization is restored. For this reason, excessive up-sizing of theMOSFET can be avoided. Namely, the MOSFET can be down-sized and madeinexpensive. In addition, the reliability of the wiper control apparatusinclusive of the driving circuit and motor can be improved.

(8) The resistance of the variable resistor is converted into a digitalvalue to define the intermittent time accurately. This improves thetiming accuracy of the intermittent wiper operation.

(9) When the VR terminal of the combination switch 2 is released, theintermittent time is accurately defined at a prescribed time by thecontroller 3. This improves the timing accuracy of the intermittentoperation.

(10) When abnormality of the short-circuiting occurs downstream of thewiper motor 7 so that the short-circuiting current flows through theMOSFET 5, the current value is limited by the presence of the currentlimiting resistor R1 so that the MOSFET 5 will not be broken.

(11) When the abnormality of short-circuiting occurs downstream of thewiper motor 7, by surely interrupting the braking circuit by the MOSFET5, the safety of the wiper control apparatus is improved. By reducingthe generated heat during the normal operation and the abnormalshort-circuiting, the wiper control apparatus can be downsized.

Although several embodiments were explained, the present inventionshould not be limited to them, but can be realized in severalmodifications and applications.

In another embodiment of the wiper control apparatus according to thepresent invention, as shown in FIG. 3, a gate circuit for the N-channelMOSFET 4, which serves as a semiconductor switch for supplying orinterrupting the driving voltage applied to the wiper motor 7, isprovided with an over-heating interruption/protection circuit 30. Theover-heating interruption/protecting circuit 30 includes a temperaturedetecting circuit, a gate interruption circuit and a latch circuit.

More specifically, in the over-heating interruption/protection circuit30, as seen from FIG. 4, the temperature detecting circuit comprises acurrent source 31, a temperature detecting portion 32, a resistor 33, areference voltage source 34, a resistor 35 and a comparator 37. Thecurrent source 31 is connected to the gate of the MOSFET 4 to which thecontrol signal is supplied from the control output FET-a of thecontroller 3 through a resistor 40. The temperature detecting portion 32comprises a plurality of diodes connected in series for detecting heatdissipation of the MOSFET 4. The connecting point of the current source31 and the temperature detecting portion 32 is connected to the minusinput terminal of the comparator 37 through the resistor 33. A referencevoltage source 34 is connected to the plus terminal of the comparator 37through the resistor 35. In operation, the comparator 37 compares thevoltage at the connecting point supplied to the minus terminal and thereference voltage from the reference voltage source 34 supplied to theplus terminal to produce a comparison result as a temperature detectedoutput.

The clock input terminal of a D-type FF (flip-flop) 38 serving as thelatch circuit is supplied with the temperature detected output from thetemperature detecting circuit. The D input terminal of the D-type FF 38is supplied with the control signal from the control output FET-a of thecontroller 3. The output from the Q output terminal of the D-type FF 38is supplied to an N-channel MOSFET 39 which is connected between thesource and gate of the MOSFET 4 and serves as the gate interruptioncircuit. Zener diodes 41 and 42 which are reverse-connected constitutean excessive voltage protection means for preventing an excessivevoltage from being applied to the MOSFET 4. Incidentally, the D-type FF38 can be omitted. In this case, the temperature-detected output fromthe temperature detecting circuit causes the N-channel MOSFET 39 servingas the gate interrupting circuit to perform the interruption operationdirectly.

When the wiper motor produces the abnormality such as locking or shortwhile it is energized, a large current flows through the MOSFET 4. Inthis case, a voltage based on the heat dissipation of the MOSFET 4 isdetected by the temperature detecting portion 32. If the voltagedetected by the temperature detecting portion 32 exceeds the referencevoltage from the reference voltage source 32, the high level outputwhich is a comparison result by the comparator 37 is supplied to theclock input terminal of the D-type FF 38. Thence, the high level outputfrom the Q output of the D-type FF 38 is applied to the gate of theMOSFET 39 so that the MOSFET 39 turns on. When the MOSFET 39 turns on,the gate potential of the MOSFET 4 becomes the low level so that theMOSFET 4 turns off. Thus, the energization of the wiper motor 7 isinterrupted.

Through the protection operation described above, the abnormal currentceases to flow through the wiper motor so that the reliability of themotor, wire and connector can be improved. The various kinds ofprotection operations may be combined as occasion demands.

As a further embodiment of the wiper control apparatus according to thepresent invention, as shown in FIG. 9, the present invention can beapplied to a wiper control apparatus in which a two-speed wiper motor isdriven. The two-speed wiper motor is commonly employed for a wiper forthe front glass of a vehicle.

As seen from FIG. 9, the wiper control apparatus according to thisembodiment comprises a combination switch 2D, a controller 3D, MOSFETs4, 5, a Zener diode 6, a two-speed wiper motor 7A, a washer motor 9, avariable resistor 10 and a current limiting resistor R1.

The combination switch 2D includes an FET terminal connected to thedrain of the MOSFET 4 and source of the MOSFET 5, an LO terminalconnected to the low speed terminal of the wiper motor 7A, an AMP-INterminal connected to the INT2 terminal of the controller 3B, an HIterminal connected to the high speed terminal of the wiper motor 7A, aGND terminal connected to ground and a WASH terminal connected to thewasher motor.

The controller 3D has an arrangement in which the ON input is omittedfrom the arrangement of the controller of FIG. 1.

In the configuration shown in FIG. 9, during the intermittent operation,the wiper motor 7A is driven by the MOSFET 4 at the same timings asshown in FIG. 5. The low speed continuous rotation and high speedcontinuous rotation are directly on/off controlled by the LO terminaland HI terminal of the combination switch 2D. During the low speedcontinuous rotation (LO) and the high speed continuous rotation (HI) ,the MOSFET 4 is separated from the wiper motor 7A by the FET terminal ofthe combination switch 2D. When the IG switch 12 is turned on with thewiper remaining on the windshield glass, even with the combinationswitch 2D being at the OFF position, the wiper motor 7A is driven by theMOSFET 4 until the wiper reaches the park position.

In this way, the low speed continuous driving (LO) and the high speedcontinuous driving (HI) are directly on/off controlled by the LOterminal and HI terminal of the combination switch 2D, the currentrating of the MOSFETs 4 and 5 can be made small. Thus, these MOSFETs canbe downsized and made inexpensive. Further, during the LO driving and HIdriving, since the MOSFETs 4 and 5 are separated from the wiper motor 7,these MOSFETs are not influenced by the electromotive force of the wipermotor coil. This makes it unnecessary to add a protection element.

In a further embodiment, the wiper control apparatus according to theinvention can be applied to a control apparatus combined with a relay.Where two systems of wipers are installed in a vehicle, the wipercontrol apparatus according to the present invention can be adopted inthe one system and the relay type wiper control apparatus according theprior art can be adopted in the other system.

In this case, as seen from FIG. 10, the wiper control apparatusaccording to the present invention and the relay-type wiper controlapparatus are combined with each other. The former comprises a controlsection 1 including a combination switch 2, controller 3B, MOSFETs 4, 5,a Zener diode 6 and a current limiting resistor R1; a wiper motor 7, anAS switch 8 and a washer motor 9. The relay-type wiper control apparatuscomprises a combination switch (inclusive of a variable resistor 10A), atwo-speed type wiper motor 7A, an AS switch 8A, a washer motor 9A and arelay 60.

The combination switch 2B includes an AS terminal connected to an ASswitch 8A through a relay 60, an LO terminal connected to a low speedterminal of a wiper motor 7A, an AMP-IN terminal connected to the INTterminal of a controller 3B, an HI terminal connected to the high speedterminal of a wiper motor 7A and a GND terminal to ground and WASHterminal connected to the washer motor 9A.

The controller 3B, in addition to the controller 3 shown in FIG. 1,includes an IG 2 terminal connected to a fuse 13A for supplying a powersupply voltage to the wiper motor 7A, a RLY terminal connected to a coilof a relay 60, an WS2 terminal connected to the WASH terminal of thecombination switch 2B, an INT2 terminal connected to the AMP-IN terminalof the combination switch 2B, an VR2 terminal connected to the VRterminal of the combination switch 2B and a GND terminal. The controller3B serves to control both MOSFETs 4, 5 and relay 60.

For example, the wiper motor 7A of the relay-type wiper controlapparatus having a conventional arrangement serves to drive a frontwiper and the wiper motor 7 of the wiper control apparatus according tothe present invention severs to drive a rear wiper.

In this way, the controller 3B includes the collected function ofcontrolling both MOSFETs 4, 5 and relay 60, and hence can be down-sizedand made inexpensive. The control is correlated between the front wiperand rear wiper.

In a further embodiment of the wiper control apparatus according to thepresent invention, the MOSFET 5 for braking the wiper motor may be anN-channel type instead of the P-channel type. In this case, as shown inFIG. 11, the gate of the N-channel type MOSFET 5 must be connected to avoltage multiplying means such as a boot strap circuit, a charge pumpcircuit, etc. Since the N-channel MOSFET has small ON resistance ofabout half the P-channel type MOSFET, with the same rating of the ONresistance, it can be down-sized or made inexpensive more largely thanthe P-channel type.

What is claimed is:
 1. A wiper control apparatus comprising: acombination switch for setting an operation mode of a wiper; a wipermotor which is driven according to the operation mode set by saidcombination switch; an autostop (AS) switch for producing a signalhaving a level varying according to a park position and other positionsas the wiper motor rotates; a first semiconductor switch element forcontrolling the on/off energization of the wiper motor; a secondsemiconductor switch element for turning on a closed circuit for brakingsaid wiper motor which passes a reverse current through said wiper motorwhile energization for said wiper motor is off; a controller forsupplying a first ON/OFF control signal to the first semiconductorswitch element and a second ON/OFF control signal to said secondsemiconductor switch element; and current limiting means for limiting acurrent flowing through said second semiconductor switch element.
 2. Awiper control apparatus according to claim 1, wherein said controllermonitors a level change in a signal from said autostop (AS) switch andwhere the level change occurs while the wiper stops, said controllerinterrupts said second ON/OFF control signal when the number of thelevel changes reaches a prescribed number of times.
 3. A wiper controlapparatus according to claim 1, wherein said first semiconductor switchelement is an N-channel MOSFET, and said second semiconductor switchelement is a P-channel MOSFET.
 4. A wiper control apparatus according toclaim 3, wherein a Zener diode is connected to said first semiconductorswitch element.
 5. A wiper control apparatus according to claim 1,wherein said first semiconductor switch element is located downstream ofsaid wiper motor.
 6. A wiper control system comprising a wiper controlapparatus according to claim 1 and a relay-type wiper control apparatus,wherein said controller controls the operation of both wiper controlapparatus and relay-type control apparatus.